The invention relates to a process for the production of a flexible polyamide composition containing at least 50 parts by weight of non-crosslinked rubber per 50 parts by weight of polyamide. Such a composition is known from U.S. Pat. No. 5,003,003. U.S. Pat. No. 5,003,003 describes that compositions containing at least 50 parts by weight of rubber per 50 parts by weight of polyamide only have good mechanical properties if the rubber is crosslinked during the mixing in the melt of the polyamide and rubber phases; the rubber is then also said to be xe2x80x98dynamically vulcanizedxe2x80x99. If the rubber is not crosslinked during the mixing in the melt, the composition""s tensile strength, among other things, will be many times lower. Especially in the case of polyamides with relatively high melting points, that is, higher than approx. 220xc2x0 C., the process of dynamic vulcanization is particularly difficult to realize without the employed crosslinking agents, generally phenolic resins, damaging the polyamide, and the vulcanization process is difficult to control. The rubber/polyamide compositions obtained via dynamic vulcanization are for these reasons generally discoloured and cannot be used in colours other than black.
The object of the invention is hence a process for the production of a flexible polyamide composition containing at least 50 parts by weight of non-crosslinked rubber per 50 parts by weight of polyamide, which has good mechanical properties and is not, or not appreciably, discoloured.
The inventors have achieved this object with a process in which
A. 30-50 parts by weight of at least one polyamide and
B. 70-50 parts by weight of a rubber composition containing at least one functionalized rubber, are mixed with one another in the melt phase, in which A+B=100 parts by weight, characterized in that the polyamide has a molecular weight such that the melt viscosity of the polyamide, measured at low shear at the temperature at which the polyamide and the rubber are mixed in the melt, is lower than about 300 Pa.s and the rubber composition""s Mooney viscosity ML (1+4) 125xc2x0 C., measured according to ISO 289-1985-(E), is at least 40. Preferably the polyamide""s melt viscosity is lower than 200 Pa.s, even more preferably 100 Pa.s, and the rubber""s Mooney viscosity is at least 50, even more preferably at least 55. Most preferably the rubber composition has a Mooney viscosity of at least 60. The inventors have found that when the polyamide""s molecular weight is chosen to be low enough, and the Mooney viscosity high enough, a good dispersion of the rubber in the polyamide matrix is most surprisingly obtained. In the case of the production of a polyamide/rubber composition the polyamide of which has a low melting point, a rubber with a relatively low Mooney viscosity, above the indicated minimum value, will generally suffice. In the case of compositions containing a polyamide with a high melting point the rubber will have to have a higher Mooney viscosity. Likewise, if, in the case of a polyamide with a low melting point, the rubber has a sufficiently high Mooney viscosity, a higher molecular weight will usually suffice than in the case of a polyamide with a high melting point. Instead of the Mooney viscosity also the melt viscosity of the rubber at the temperature of melt mixing at high shear may be chosen as a parameter. However these data are not available for most materials. Anyhow under the conditions of melt mixing the melt viscosity of the rubber composition should be appreciably higher than the melt viscosity of the polyamide.
By carrying out systematic experiments, an average person skilled in the art will be able to find the right combinations of the polyamide""s molecular weight and the rubber""s Mooney viscosity within the indicated molecular weight and Mooney viscosity ranges for the combination of polyamide and rubber desired in his case.
The usual equipment can be used for the mixing in the melt, for example a Brabender mixer, a Haake or Busch kneader or an extruder, for example a single- or double-screw extruder. Preferably a double-screw extruder, excerting high shear, is used. To prevent the risk of the polyamide suffering thermal damage, the process is preferably carried out in an inert gas atmosphere.
Rubber composition B preferably contains a combination of at least one functionalized rubber and a non-functionalized rubber. As used herein rubber means a low modulus flexible polymer with a glass transition below 0xc2x0 C., preferably below xe2x88x9225xc2x0 C. Examples of polymers falling under this definition are copolymers of ethylene and xcex1-olefins, for instance propylene and butylene. Also the new group of plastomers, copolymers of for instance ethylene and 1-octene, obtainable by polymerisation in the presence of a metallocene catalyst are usefull as a component of composition B. xe2x80x98Functionalized rubberxe2x80x99 is understood to be a rubber containing groups that can react with polyamide. Such functionalized rubbers are known. A very large number is for example described in U.S. Pat. No. 4,174,358, as are the methods for preparing these functionalized rubbers. Various functionalized rubbers are commercially available under different names. Very suitable are rubbers that have been chemically modified through reaction with maleic anhydride or graft-copolymerisates of the rubber and an unsaturated dicarboxylic acid anhydride or dicarboxylic acids and/or esters, for example maleic anhydride, itaconic acid and itaconic anhydride, fumaric acid and maleic acid or a glycidyl acrylate, for example glycidyl methacrylate. In such a case the polyamide preferably contains sufficient amino end groups that can react with the functional groups. As the molecular weight of the polyamides that can be used in the process according to the invention is relatively low, the number of available amino end groups is generally high enough.
In principle, any non-crosslinked rubber that meets the Mooney viscosity requirements is suitable for use in the process according to the invention. xe2x80x98Non-crosslinked rubberxe2x80x99 is understood to be a rubber that is substantially non-crosslinked and shows no typical elastic behaviour. In the practice of mixing in the melt at high temperatures some crosslinking can generally not be prevented. Preferably the gel content is less than 50%, more preferably less than 30%, even more preferably less than 10%. The gel content is here defined as the fraction of the rubber that is insoluble in the solvent suitable for the rubber in question. For an EPDM rubber a suitable solvent is for instance xylene.
As B, use is preferably made of a combination of an ethylene-xcex1-olefin copolymer, for example an ethylene-propylene copolymer, EPM, rubber and an ethylene-xcex1-olefin terpolymer whose third monomer is a non-conjugated diene, for example a norbornene, for example ethyl norbornene, or hexadiene, for example-ethylene-propylene-norbornene terpolymer, EPDM rubber. In this case both the EPM and the EPDM may be functionalized. Preferably a combination of a non-functionalized EPDM rubber and a functionalized EPM rubber is used. In the case of polyamide 6 the functionalized EPM rubber has preferably been functionalized with maleic anhydride (MAh). Known EPDM rubbers are for example commercially available under the trade names Keltan from DSM NV, Nordel from E.I. du Pont de Nemours and Company, and Royalene from UniRoyal.
MAh-functionalized EPM rubbers are for example Exxelor VA 1801(copyright) made by Exxon and Tafmer MP 0610(copyright) of Mitsui.
The MAh content of the functionalized rubber may vary within a wide range, for example between 0.1 and 10 wt. %, preferably between 0.1 and 5 wt. %, more preferably between 0.1 and 2 wt. %. The weight ratio of the functionalized and non-functionalized rubbers may vary within a wide range, for example between 1:10 and 10:1; preferably the ratio is chosen to be lower than 1, for example between 0.9 and 0.1.
Very surprisingly compositions with superior properties are those in which at least one of the components of the rubber composition B is a styrene butadiene based block copolymer or functionalized styrene-butadiene block copolymer. This kind of elastomeric block copolymers is for instance commercialized under the tradename Kraton by Shell.
The flexible polyamide composition, obtainable with the process according to the invention, comprises
A: 30-50 parts by weight of at least one polyamide
B: 70-50 parts by weight of at least one non-crosslinked rubber, with A+B=100 parts by weight, and is characterized in that the rubber phase is dispersed as discrete particles in the polyamide as a continuous phase. The particle size of the dispersed rubber is generally smaller than 5 xcexcm, preferably smaller than 3 xcexcm. Preferably 90% of the number of rubber particles is smaller than 1 xcexcm. The presence of A as a continuous phase does not exclude the possibility of a minor amount of A, for example up to 10% of A, being incorporated in B as small particles.
Preferably the flexible polyamide composition contains a rubber composition B consisting of
b1: at least one non-functionalized rubber and
b2: at least one functionalized rubber.
In such a case the dispersed rubber particles preferably have a nucleus consisting of the non-functionalized rubber and a shell consisting of the functionalized rubber.
The flexible polyamide composition according to the invention differs from the known polyamide compositions containing at least 50 wt. % non-crosslinked rubber such as those for example disclosed in U.S. Pat. No. 5,003,003 in that it is significantly more resistant to oil. For example, for an A:B=4:6 composition the increase in volume after 7 days"" contact with ASTM 3 oil at 100xc2x0 C. is even less than 10%, while for a similar composition according to the state of the art the increase is more than 100% after only 3 days"" contact with oil (see example 6B of U.S. Pat. No. 5,003,003). This significantly better resistance to oil is a simple confirmation of the fact that the rubber particles are contained in a polyamide matrix.
Preferably the flexible polyamide composition according to the invention contains polyamide in a minor fraction for instance A being at most 45 pbw even more preferably at most 40 pbw, thereby imparting a higher flexibility without significant loss of oil resistance.
In the process for the production of a flexible polyamide composition according to the invention it may be advantageous to use a plasticizer for the polyamide phase. This will make it possible to use polyamides with a higher molecular weight than without the plasticizer. With this process a lower shore hardness is moreover obtained for the compositions. Examples of plasticizers for the polyamide phase are nonyl phenol and butyl benzenesulphonamide. The plasticizer is generally used in an amount of between 1 and 15 parts by weight, preferably 2-10, per 100 parts by weight of polyamide.
In a different case it may be advantageous, for example in order to improve the tensile strength, to subject the composition to after-condensation, preferably in the solid phase, after the mixing in the melt. Such a process can however not be used without limitations because there is a risk of phase inversion or separation into two cocontinuous phases during the processing of the composition by means of for example injection-moulding.
The composition according to the invention may furthermore contain the additives commonly used for polyamides, for example stabilizers, flame retardants, processing aids such as release agents and colourants or pigments. For specific applications the composition may optionally contain reinforcing fibres, for example glass fibres. The rubber phase may contain the additives commonly used for rubber and may for example be diluted with oil to a limited extent.
The composition according to the invention can preferably be used in processing methods involving low shear forces, for example in the extrusion of tubes, hoses, cable sheaths, in blow-moulding processes, fibre spinning and injection moulding.
The composition of the invention presents a particular advantage for application in the production of polyamide inlet manifolds for internal combustion engines, in which a flexible zone can be incorporated in a sequential blow-extrusion process, which facilitates the installation of the manifold. The strength of the welds between the glass-fibre-reinforced stiff parts and the flexible part is of good quality because in all the parts the continuous phase is polyamide.
The composition of the invention presents a further advantage in applications in which a hard polyamide core is to be coated with a soft flexible layer, also called a xe2x80x98soft-touchxe2x80x99 layer. Such an application is to be found for example in tool handles and tool casings. This multi-layer structure with very good adhesion between the two layers can be obtained through coextrusion or sequential injection moulding.
The good resistance to oil of the composition according to this invention presents additional, and often essential, advantages in applications such as those mentioned above.